275 
Bower. — Studies in the Phytogeny of the Filicales . 
were in two specific cases only 251 and 319. This smaller number is in 
accord with the smaller size of the pear-shaped sporangia of the latter 
species, but it is nearly matched by the output in species of Eu-Gleichenia , 
where the relatively large sporangia produce large spores, but their 
numbers are in near proximity to the typical number 256. 
A more special interest, however, attaches to the case of G. pectinata , 
which is sorally, as it is also anatomically, the most advanced species. It 
has long been known that the sori of this species contain the largest 
number of sporangia in the genus. Hooker ( 5 Syn. Fil. ’, p. 15) mentions 
‘ 8-10 capsules ’. The drawing (PL XXX, Fig. E) shows that this is clearly 
under the mark, for the numbers vary from 10 to 15 in this specimen from 
Jamaica not specially selected. The sporangia, being long-stalked and all 
seated upon a central and slightly raised receptacle, are obviously crowded. 
They form two tiers, the upper tier fully occupying the central space, which 
in Mertensia is usually vacant. The enlarged drawing of a single sorus 
(PI. XXXI, Fig. P") shows that the sporangia are even flattened against one 
another, a fact which is readily seen in their flattened sides when the 
sporangia lie separate and free. They are also far from uniform in size, 
and the orientation of the annulus is occasionally reversed. It is plain that 
shedding of the spores will here be a matter of difficulty if the median 
dehiscence is maintained. That the difficulty is a real one is shown by the 
fact that, though the sporangia arise and mature all simultaneously, many 
of them remain full long after other sporangia of the same sorus have been 
emptied. It appears then that in G. pectinata the Gleicheniaceous type of 
sorus has reached the point of ineffectiveness in its increase in number of 
the sporangia. There are four possible ways out of the difficulty, and they 
may be adopted singly or in combination: (1) by increasing the length 
of the sporangial stalk, (2) by adopting a lateral in place of a median 
dehiscence, (3) by extending the area of the sorus, and (4) by elongating 
the receptacle. But none of these has been adopted by the genus Gleichenia 
itself. Other Ferns have, however, adopted them, and have succeeded. 
The development of the sorus of G. pectinata has been followed out for 
comparison with that of other species. The receptacle is present as a consider- 
able upgrowth before the development of the sporangia begins (PL XXXIV, 
Figs. 1 , 2). The sporangia themselves are almost simultaneous in their appear- 
ance, but not perfectly so. In Fig. 3 the middle sporangium is just dividing 
off its cap-cell, whereas those right and left have them complete. There is still 
more discrepancy in the state of development of the three sporangia in 
Fig. 4. But there does not appear to be any rule or method of succession. 
The sporangia themselves show a segmentation which, though variable 
in detail, conforms to that already described for other species of the genus. 1 
In most cases it ranks most nearly with the type seen in the Schizaeaceae 
1 Compare Studies. IV. Phil. Trans., vol, cxcii, pp. 32-8, and Plate II. 
